1. Field of the Invention
The present invention relates to an apparatus for and a method of measuring and testing the physical composition of materials, but more particularly the present invention relates to an apparatus for measuring the intrinsic time constant of liquids.
2. Description of the Prior Art
Liquids whose purity or composition must be tightly controlled are essential elements in many industrial processes. Perhaps the most common example of an industrial liquid is distilled or deionized water. This purified water is produced at rates of millions of gallons per day. It is used in boilers, in steam plants, in the medical industry and in the food industry. It is also used in the semiconductor industry for cleaning and rinsing microelectronic devices. In recent years, the insulating properties of highly purified water has been exploited in the pulse forming lines of large electrical pulse power machines used in weapons and fusion research. Consequently, there is a need in the prior art, due to its wide spread use in many industrial applications, to devise apparatuses and methods to monitor the quality of water in an improved manner. A corollary need in the prior art is to be able to determine the purity of water and virtually all other liquids in an improved manner.
At the present time, the electrical property of water that is used to judge its quality is resistivity, or the reciprocal of resistivity, conductivity. The foregoing quantity and its use to judge quality can be understood by visualizing an ideal cube of liquid that is 1 centimeter per face. Now if a voltage V of 1 volt is impressed between two electrodes disposed tangent to and contacting two opposing faces of the cube so that a uniform current I of 1 ampere flows through the electrodes, and, accordingly, through the cube portion of the liquid, then the liquid is said to have a resistivity .pi. of 1 ohm-cm. Generally, for a particular electrode configuration: ##EQU1## where X is a geometric factor which depends on the size and shape of the electrodes used in the measurement. Limitations on resistivity measurements arise from uncertainties related to the choice of the geometric factor X which can change with aging of the electrodes, the presence of bubbles in the liquid and the evolution of gases in the liquid (electrolysis, flow field uncertainties, etc.). Also, there is a need for great care in positioning the electrodes in the fluid to be measured if accurate readings are to be ascertained, and a dc voltage standard is required when making the resistivity measurements. In addition, since the resistivity, and, accordingly, its measurement in a liquid is predicated on the presnce of change carriers therein, it is sensitive only to the presence of ionic impurities in the liquid. Hence, there is a need in the prior art to configure an apparatus and to devise a method to measure another electrical property of liquids termed the intrinsic time constant .tau. so as to judge the quality of substantially all liquids, but yet not be limited to those having substantial ionic impurities therein, while eliminating all of the limitations and problems associated with the measurement of the resistivity .rho..